Geochemistry Laboratories

Geochemistry Standards

Overview

In the mid-1980s, the Chevron Oil Field Research Company worked with the International Atomic Energy Agency to develop a suite of three natural gas standards for molecular and stable isotopic analyses. These reference materials included a coal-associated gas (NGS1), an oil-associated gas (NGS2), and a biogenic gas (NGS3) [1]. NGS-1 was collected by G. Hut (University of Groningen, The Netherlands) from the Groningen gas field in the northeastern part of the Netherlands, and consists of more than 80 % CH4 with a δ13C value of approximately –29 ‰ (VPDB). NGS-2 was collected by T. Ricchiuto (Agip S.p.A., Milano, Italy) from southern Italy and contains more than 50 % CH4 with a δ13C value of approximately –45 ‰ (VPDB). NGS-3 was also collected by T. Ricchiuto (Agip S.p.A., Milano, Italy) from the Porto Corsini field, Po Valley in northern Italy, and contains more than 95 % CH4 with a δ13C value of approximately –73 ‰ (VPDB).

In the early 1990s, these reference gases were transferred to the US National Institute of Standards and Technology (NIST), which provided recertified isotopic values, assumed responsibility for distribution, and renamed them RM 8559, RM 8560, and RM8561, respectively [2]. For more than twenty years, these materials were distributed by NIST, and used in research and technology development by industry, academia, and governmental agencies. Further details related to the development of these standards may be found in Wise and Watters, 2007 [2].

By the mid-2000s, the supply of these gases had diminished and NIST discontinued the distribution of these materials. The residual gas, cylinders, and manifold assembly were originally transferred to a private research institution (Power, Environmental, and Energy Research Institute in Covina, CA), but subsequently were moved to the US Geological Survey (USGS) Energy Resources Geochemistry Laboratories located in Denver, Colorado. Around this time, a “round-robin” type inter-laboratory study of some natural gases from China was conducted [3], with the hope that these may replace the NIST standards. However, this study was not a true calibration exercise, and the gases were not made available for general use as reference standards.

In response to this situation, the Energy Resources Program of the USGS undertook a project to develop a new suite of gas standards to replace the old NIST gas standards. An undertaking of this magnitude is beyond the capabilities of the USGS alone, and consequently, this project was a collaborative effort by researchers from academic, governmental, and industrial organizations from around the world. USGS personnel took the lead to administer and coordinate all of the work related to the development of these standards; however, much credit is due to numerous individuals from outside the USGS who contribute valuable time and resources to the successful completion of this project.

Standard Development

Technical Advisory Committee

The first step in the development of these gas standards was to organize a technical advisory committee of natural gas experts from academic, industrial, and governmental agencies from around the world. Twenty eight individuals agreed to serve as formal members of this committee, which helped review and advise on all important aspects of the project including:

• The determination of the number and the molecular and isotopic composition of the gases used as reference materials.
• The choice of subsampling and sample distribution methods.
• The selection of the analytical methods used for the calibration of the gases.
• The evaluation of the analytical data.

The members of the technical advisory committee are listed below (Table 1). All aspects of the standard reference gas development were reviewed by the advisory committee. Due consideration was given to all recommendations, and every effort was made to comply with the consensus view of the committee. The USGS is indebted to all of the members of the advisory committee for their contribution to the successful development of these standards. Although the committee provided valuable oversight throughout the development of the standards; ultimately, the USGS is solely responsible for the scientific integrity of the standard gases and the process that led to their development.

Table 1: Natural Gas Standards Advisory Committee

Name

Institution

Organization Type

Geographic Region

Robert Dias, Co-Chair

U.S. Geological Survey

Government

North America

Geoffrey Ellis, Co-Chair

U.S. Geological Survey

Government

North America

Alexandre de Andrade Ferreira

Petrobras

Industry

South America

Andy Bishop

Shell Oil

Industry

North America

Junhong Chen

Geoscience Australia

Government

Asia

Dennis Coleman*

Isotech Laboratories

Industry

North America

Tyler Coplen

U.S. Geological Survey

Government

North America

Jingxing Dai

PetroChina

Industry

Asia

Giuseppe Etiope

Instituto Nazionale di Geofisica e Vulcanologia

Government

Europe

Brian Giebel*

National Institute of Standards and Technology

Government

North America

Maciej Kotarba

AGH University of Science and Technology

Academia

Europe

Michael Lawson

ExxonMobil

Industry

North America

Christy Legner*

Isotech Laboratories

Industry

North America

Fang Lin

Chevron

Industry

North America

Steve Pelphrey

Isotech Laboratories

Industry

North America

Alain Prinzhofer

IPEX

Industry

South America

Elin Rein

StatOil

Industry

Europe

Karyne Rogers

GNS Science

Government

Asia

Arndt Schimmelmann

University of Indiana

Academia

North America

Stefan Schloemer

Federal Institute for Geosciences and Natural Resources (BGR)

Government

Europe

Martin Schoell

Gas Consult International

Industry

North America

Stephen Sestak

CSIRO

Government

Asia

Barbara Sherwood Lollar

University of Toronto

Academia

North America

Yongchun Tang

Power, Environment, and Energy Research Institute

Industry

North America

Bruce Vaughn

University of Colorado

Academia

North America

Andrea Vieth-Hillebrand

GeoForschungsZentrum

Government

Europe

Michael Whiticar

Unversity of Victoria

Academia

North America

John Zumberge

Geomark

Industry

North America

*Left committee before project was completed.

Standard Gas Sample Selection

After extensive consultation with the technical advisory committee, the ideal molecular and stable isotopic compositions of the new standard reference materials were identified (Table 2). The targeted compositions and values represent a series of compromises among selection of specific compounds, identification of the most useful isotopic range, and the sheer volume of work required to provide a proper calibration. The inclusion of non-hydrocarbon gases (particularly N2 and CO2) was considered and determined not to be a priority given the availability of other standards for these compounds. Furthermore, heavier hydrocarbon homologues (specifically iso- and normal butanes and pentanes) were discussed as additional potential compounds of interest for inclusion in these standards. Although standard reference materials for the stable isotopic composition of butane and pentane gases do not currently exist, the consensus view of the committee was that the potential negatives associated with inclusion of these compounds outweighed the benefits. In particular, the heavier hydrocarbon components present a risk of phase separation under certain pressure and temperature conditions which complicates the storage, handling, and distribution of the standards. Moreover, it was difficult to justify the significant increase in the amount of analytical work required to calibrate these additional components when most analytical methods used to determine their stable isotopic composition are directly tied to methane, ethane, or propane.

It was determined that "synthetic" gas mixtures were more likely than produced natural gas samples to be able to meet the desired criteria (Table 2), and that, to the extent possible, the new gas standard mixtures should be fabricated from pure components with the desired isotopic compositions. The molecular compositions of the three mixtures were selected such that the gas components were equimolar on a carbon basis to facilitate the stable isotopic analysis of the standards by modern continuous-flow GCirMS methods.

Mix 1 – light: After an exhaustive attempt to identify a method for fabricating an isotopically light mixture that closely matched the target composition, it was determined that using a produced natural gas would be the most cost-effective method for obtaining this gas mixture. The closest match to the target composition for the isotopically light gas mixture that could be found was a produced natural gas sample from a biogenic gas field in Northern Colorado. It was concluded that this gas was the best material that could be obtained for the isotopically light end-member standard, given the fiscal and logistical constraints of the project. The mole % composition of the gas is typical of a natural bacterial gas and is labeled as USGS HCG-3 (U.S. Geological Survey Hydrocarbon Gas 3)

Mix 2 – intermediate: The intermediate gas mixture was created by locating sources of the pure component gases that had stable isotopic compositions that most closely matched the target compositions. These pure components were then blended together in the desired proportions to create the intermediate gas mix. Although the d2H of the ethane in this mix is significantly heavier (~50‰) than the target value, this was the lightest value that could be found. Given the difficulty associated with trying to create isotopically depleted compositions, it was determined that this was as close to the target values for the intermediate mix as was feasible. This intermediate gas mixture has been labeled USGS HCG-2.

Mix 3 – heavy: The heavy gas mixture was created by adding small aliquots of isotopically enrichCed (13C and 2H) methane, ethane, or propane into additional cylinders of the pure components that were used to make the intermediate mix. These heavy components were then blended together to make the heavy gas mix, USGS HCG-1.

Analytical Methods

The calibrated values for the gas standards were derived from analytical work performed at the USGS Energy Geochemistry Laboratory in Denver, Colorado and Isotech Laboratories, Inc. in Champagne, Illinois. The hydrocarbon gas analytes were directly measured against the inorganic carbonate standards NBS-19 and LSVEC for carbon and the SMOW-SLAP scale for hydrogen.

Both laboratories were provided duplicate pressurized stainless steel cylinders of the individual components (methane, ethane, and propane) that comprise the mixtures USGS HCG-1 and HCG-2, for a total of twelve (12) individual gas samples. These gases were prepared for dual-inlet isotopic analyses on a manual vacuum line. Briefly, this involved the combustion of the individual hydrocarbons to CO2 and water and the subsequent reduction of water to H2 by zinc reduction (400°C, 60 min).

The isotopically light gas-standard (USGS HCG-3) is a produced natural gas from a biogenic gas field in northern Colorado. As such, it contains a mixture of methane, ethane, and propane and required splitting into the component hydrocarbon gases prior to offline combustion and analysis. The component isolation from this gas mixture was done at Isotech Laboratories by means of a preparatory GC system. This gas mixture was split into the individual hydrocarbon gases, combusted to carbon dioxide and water, and distributed to the USGS laboratory for analysis. A total of eighteen (18) glass ampoules (one carbon dioxide and one water sample for each of methane, ethane, and propane, each in triplicate) was distributed to the USGS laboratory for reduction of the water to hydrogen gas for d2H analysis of the hydrogen and d13C analysis of the carbon dioxide. Similar sample preparation (i.e., water reduction to H2) and analysis was performed at Isotech Laboratories, Inc.

Additionally, samples of the NGS gases (NIST RM 8559, RM 8560, and RM8561) were prepared and analyzed by the same methods as the USGS gas standards. This allows for the new reference gases to be directly tied to the NGS gases previously in circulation.

The carbon and hydrogen stable isotopic composition of the CO2 and H2 derived from the combustion of the hydrocarbon gases and subsequent reduction of water were measured by dual-inlet magnetic-sector isotope ratio mass spectrometry (Thermo MAT253). The CO2 was analyzed directly against CO2 produced from the H3PO4 digestion (30°C, 24h) of NBS 19. The H2 gases were analyzed against SMOW and SLAP prepared (reduced to H2) by the same method as the hydrocarbon-derived water. Each sample and primary standard was analyzed in replicate in order to establish the statistical significance of each result. The arithmetic mean of the replicate analyses of each individual component is taken as the calibrated value for the gas standards as reported in Table 3.

Table 3. Suggested reference values for the new USGS hydrocarbon gas mixtures. These values are solely based on offline preparation methodology and dual inlet analyses. The isotope values for carbon are relative to VPDB, and for hydrogen are relative to VSMOW. The mole percent compositions are not calibrated and are for informational use only.

­­­

USGS HCG-1

USGS HCG-2

USGS HCG-3

d13C

d13C

d13C

C1

C2

C3

C1

C2

C3

C1

C2

C3

Avg.

-1.51

-10.22

-15.43

-43.09

-29.80

-19.35

-61.39

-45.31

-36.80

Std. Dev.

0.08

0.03

0.10

0.10

0.04

0.09

0.12

0.06

0.06

n

12

21

21

30

21

21

6

6

6

d2H

d2H

d2H

C1

C2

C3

C1

C2

C3

C1

C2

C3

Avg.

-64.0

54.3

74.6

-183.2

-125.6

-171.0

-224.3

-262.2

-245.2

Std. Dev.

3.1

4.6

7.6

5.7

1.9

2.0

3.2

3.0

2.3

n

12

21

18

29

21

20

6

5

6

C1

C2

C3

C1

C2

C3

C1

C2

C3

~mol %

46

43

11

59

33

8

93.5

1.2

0.4

Ordering

Placing an Order

Sub-sampling of the standard gas tanks and distribution of the samples only takes place two times per year (assuming that there are orders to fill). This is typically in April and October of each year; however, exact dates vary. Orders will be accepted at any time. Given the limited quantity of gas available, purchasers are restricted to one purchase every three years. Gases are distributed in 50 mL stainless steel vessels equipped with one (1) standard ¼” NPT fitting and pressurized to approximately 50-75 psi. At this time, gases must be ordered as a set of all three standard reference materials. Individual reference gases may be offered for sale at some later date. Technical questions related to the gas standards and information regarding placing an order should be directed to:

The next fill period will be October 2017; Cut-off for orders will be October 1, 2017

Individuals requesting to place an order for the gas standards will receive an order form to be completed in full and returned to Mirian Cuara via regular mail or fax. A user agreement form will then be sent to the purchaser for signature and must be returned to Ms. Cuara. Purchases by other agencies of the U.S. Government must be identified prior to completing the order form, as separate procedures apply.

User Agreements

In order to comply with the United States Economy Act, 31 USC 1535A, the USGS Technology Transfer Office requires that all purchasers of USGS natural gas standards complete and sign an agreement stating that the acquisition of the reference materials from the USGS falls within the authority of the agency to enter into cooperative research and development agreements. User agreement forms will be sent with blank order forms and should accompany each order.

Shipping

The USGS will arrange and cover the cost of shipping for orders within the US and Canada. International orders are not currently being accepted. It is anticipated that international orders will be accepted in the near future; however, the purchaser will be responsible for making all of the arrangements and covering all of the expenses associated with international sample shipping. If special packaging and labelling are required, it will be the responsibility of the purchaser to notify the USGS and, if requested, supply any additional shipping materials. There are private companies that, for a fee, will make all of the arrangements for international shipping of hazardous materials such as these gas samples. The USGS may be able to refer purchasers to these third parties, but in no way endorses any particular company, nor is in any way responsible for their performance or actions. Currently, only orders from U.S. entities are being accepted for processing.

Payment Options

Domestic/International CustomersPayments can only be made online through ACH (Pay.gov)

USGS Customers
Payments will be handled through VA transfer

Other Federal Agencies
Payments will be handled via IPAC through Treasury

Certificates

Preliminary Certificate of Analysis

A full report on the development and certification of the natural gas standards is currently in preparation. A preliminary certificate of analysis containing the calibrated values of the gas standard is available here: USGS Natural Gas Standards Certificate

Database Download

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